Infrared imaging optical systems are typically used to view and image light energy in the infrared optical spectrum. The production of infrared light is typically associated with the production or release of heat by hot objects such as engines and living mammals, such as for example human beings.
Infrared energy is capable of transmission through many conditions which would otherwise block visible light, such as clouds of particulate matter, water vapor, vegetation covering and various forms of optical camouflage. With respect to engines and the heat of mechanical or chemical systems, infrared detection can be highly beneficial.
Missiles fired at an aircraft may be detected by the heat and corresponding infrared signatures produced by their engines regardless of whether the missile is guided by an active or passive targeting system. Aircraft that are potentially targets for such missiles may carry infrared warning devices that view the exterior world in search of heat signatures that are associated with the engines of such missiles. Upon the detection of such a missile, such systems provide advance warning to the pilot and crew.
These sorts of detection systems may be enhanced by the ability to clearly detect and resolve an infrared emitting object, but in many instances mere detection is sufficient. However, there are a growing number of instances where mere detection of an infrared source is not enough, rather it is highly desirable to resolve the image and clearly identify the nature of the source.
Ground based or ocean based vehicles may also emit detectable infrared signatures. Increasingly, space based or high altitude imaging systems are being utilized to image large areas of geography. Although in the past it has been common to over-fly an area repeatedly or image an area as a series of line scans, real time defense, object(s) identification and tracking may preclude or at least significantly diminish the value of such systems.
So as to achieve a large field of view, and therefore attempt to permit large area imaging as a single operation, optical systems employing an inverse-telephoto lens, sometimes termed a “fisheye” lens, may be employed. Such systems typically have a constant angular resolution across their entire field of view.
The image gathered by such a fisheye lens is typically provided to the focal plane of an infrared detector. The focal plane is typically an array of small pixels, each being operable to generate or pass a current in response to infrared radiation being incident upon the pixel. By processing these generated signals it is of course possible to generate a visual representation of the infrared image, and/or perform identification processes.
Attempts have been made to develop image sensors to compensate for such image blur, as is set forth in U.S. Pat. No. 4,935,629 to Livermore et al. entitled “Detector Array for High V/H Infrared Linescanners.” It is of course also noted that Livermore does not teach an imaging system for large area simultaneous imaging, but rather is attempting to resolve a related issue of image blur that also occurs with line scanners viewing ground objects at varying distances.
Such specialized image sensors as proposed by Livermore are likely to be costly to fabricate and have very limited use beyond use in such a disclosed line scanner. As technology advances and new opportunities arise, adaptable technologies are most highly desired so as to help offset the high costs of specialized tooling and manufacturing.
Hence, there is a need for an infrared imaging optical system that overcomes one or more of the issues and problems identified above.